Effects of abomasal lipid infusion on liver triglyceride accumulation and adipose lipolysis during fatty liver induction in dairy cows

The objective was to determine the effects of abomasal infusion of linseed oil on liver triglyceride (TG) accumulation and adipose tissue lipolysis during an experimental protocol for induction of fatty liver. Eight nonpregnant, nonlactating Holstein cows were randomly assigned to treatments in a replicated 4 x 4 Latin square design. Treatments were abomasal infusion of water (W), tallow (T), linseed oil (LO), or half linseed oil and half tallow (LOT) at a rate of 0.56 g/kg of body weight per day. Each experimental period consisted of a 4-d fast concurrent with administration of treatments into the abomasum in 6 equal doses per day (every 4 h). Cows were fed ad libitum for 24 d between periods of fasting and lipid infusion. Infusion of linseed oil (LO and LOT) increased alpha-linolenic acid (C18:3n-3) content in serum (12.2, 10.4, 4.2, and 4.6 g/100 g of fatty acids for LO, LOT, T, and W, respectively), but not in the nonesterified fatty acid (NEFA) fraction of plasma. Treatments had no effect on plasma NEFA concentrations. Abomasal infusion of lipid increased in vitro stimulated lipolysis in subcutaneous adipose tissue, compared with W (4,294, 3,809, 4,231, and 3,293 nmol of glycerol released x g(-1) tissue x 2 h(-1) for LO, LOT, T, and W, respectively), but there was no difference between fat sources. Hepatic TG accumulation over 4-d fast was 2.52, 2.60, 2.64, and 2.09 +/- 0.75 mu g of TG/mu g of DNA for W, LO, LOT, and T, respectively, which did not differ. Abomasal infusion of LO did not reduce liver TG accumulation, plasma NEFA concentration, or alter in vitro adipose tissue lipolysis when compared with T. These results contrast with a previous study involving i.v. infusion of lipid emulsion derived from LO. Discrepancies might be explained by the use of different administration routes and a relatively modest induction of liver TG accumulation in the current experiment.